A method of treating a fetus or embryo suspected of having a congenital condition that involves an abnormal or missing protein, the method has the steps of a. providing a plurality of human umbilical cord blood in a form suitable for intravenous administration; a b. administering the human umbilical cord blood cells to a mother carrying a fetus of embryo suspected of having said congenital condition. Such congenital conditions include Sanfilippo's syndrome, Hunter's syndrome, Hurler's syndrome, Tay-Sachs disease, Gaucher's disease, von Gierke's disease, Pompes disease, Cori disease, Andersen disease, McArdle's disease, Hers disease, Tauri's disease or Type IX glycogen storage disease.